The present invention relates to a control apparatus and method for an internal combustion engine having a variable compression ratio mechanism.
A typical conventional ignition timing control system for an internal combustion engine is adapted to determine an ignition timing in accordance with engine speed and load.
In contrast to this, it is proposed, as disclosed in Unexamined Japanese Patent Publication No. 2001-280228, to optimize an ignition timing with consideration of valve timing. This is for taking into account decrease in combustion speed that is caused when a variable valve operating mechanism is used to perform a so-called non-throttle operation or when an internal EGR ratio (remaining gas ratio) is controlled by valve overlap. Namely, in such a non-throttle operation, decrease in combustion speed is caused when a set intake valve closing timing is advanced to decrease an effective compression ratio. Further, in such an internal EGR ratio control by valve overlap, decrease in combustion speed is caused by an increased portion of an internal EGR ratio.
On the other hand, it is proposed, as disclosed in Unexamined Japanese Patent Publication No. 2001-263114, a multi-link type variable compression ratio mechanism capable of varying a compression ratio by using a plurality of link mechanisms.
In such an internal combustion engine having a variable compression ratio mechanism, it is desirable to optimize an ignition timing in accordance with a set compression ratio similarly to the case the engine is provided with the variable valve operating mechanism.
Namely, it is desirable to perform basic setting of the ignition timing in accordance with a compression ratio (specifically, an angle of a control shaft that controls the compression ratio) that is set every combustion cycle in addition to engine speed and load.
Further, there is a technique for controlling an ignition timing in accordance with knock of the engine detected by a knock sensor. Namely, an ignition timing is controlled so as to advance from a basic ignition timing until knock of the engine is detected, and upon detection of knock the ignition timing is controlled so as to retard by an amount determined based on a frequency and magnitude of knock. In the meantime, the ignition timing control described above is performed when the engine is in an operating range in which noise added to sensor outputs is relatively small (mainly in an operating range of middle speed or lower) and in an operating range of middle load or lower in which there is a possibility of occurrence of knock. In an operating range in which engine speed is higher than middle speed, an ignition timing correction value obtained in an operating range in which the ignition timing control is performed is used as an estimation value. Further, it has been proposed to learn an ignition timing correction value in accordance with occurrence of knock (knock correction value) and control the ignition timing based upon the learned correction value. An example of an ignition timing learning control is disclosed by Unexamined Japanese Patent Application No. 5-039770. Namely, in the ignition timing learning control, an ignition timing correction value (knock correction value) is learned depending upon whether or not the engine is knocking and an ignition timing is controlled depending upon the learned correction value. Together with such an ignition timing learning control, learning of an ignition timing correction value is stopped during a predetermined number of ignition at the time of judgment of acceleration, thus realizing assured ignition timing correction based on knock of the engine.